The present invention relates to a security system including a single base unit and a plurality of security terminals, in which the individual security terminals are centrally controlled by the base unit.
Recently, security systems have been developed in which a plurality of security terminals provided in individual houses, offices, etc. are connected through cables to a base unit, and the occurrence of abnormal conditions, such as a fire, a trespasser, etc. are reported to the base or central-control center. However, since the conventional security system merely performs one-way data communication in the direction from the security terminals to the base unit to inform the latter of the occurrence of abnormal conditions, it has been impossible for means located at a particular terminal to immediately confirm whether or not the base unit safely received the information sent out from the security terminal. This is an inconvenience for the subscriber. Particularly, in a medical call (requesting the medical aid of a doctor) or in an emergency call (to convey specific comments to a designated place upon the calling a telephone number, for example), it takes a considerably long time to receive a response. During this interval, the subscriber cannot confirm if the base unit has safely received the information he has sent.